Southwest Airlines’ website and mobile app were down for about an hour Monday morning due to what the carrier described as “technical difficulties” with its reservation system, preventing passengers from booking tickets.

A company spokeswoman said the issue affected all airlines operating on the Amadeus reservation platform. The company’s website began experiencing “performance issues” shortly before 9 a.m. and was restored to full functionality around 10 a.m., spokeswoman Brandy King said in an email.

No flight operations were affected.

“We are carefully monitoring the system and will work with Amadeus as they perform a root cause analysis,” King said. “We apologize to customers for the inconvenience.”

Southwest acknowledged the outage in a tweet shortly before 9:30 a.m., as customers flooded social media with reports that they were unable to buy tickets through the website or app.

During the outage, parts of Southwest’s website were still functional, but users received an error message when trying to book an itinerary.

The issue comes on Cyber Monday, the biggest day of the year for online shopping. Southwest was one of several airlines offering special deals for Black Friday and Cyber Monday.

The company has been transitioning to a new, more modern reservation system made by Amadeus IT Group over the last year. While the company has continued to tweak the system, there haven’t been any major outages following a May switch to the new platform.